This section provides background information related to the present disclosure which is not necessarily prior art.
In groundwater wells, landfill gas recovery, landfill leachate recovery wells and condensate recovery wells, hereinafter generally referred to as “landfill wells”, there is a need to monitor gas production from the well, most commonly methane gas. Landfill wells commonly produce flow rates of methane gas that are collected for off-site delivery and use. Normally, gas flow rates ranging from approximately 5 to 150 cubic feet per minute (CFM) are achieved from individual wells. Maximum gas flow rates ranging from 200 to 250 CFM are also known. Removal of methane gas is required to maintain the safety and stability of the landfill. Withdrawal of methane gas is commonly assisted using vacuum pumps located on-site at the landfill. Landfills are required to periodically measure and maintain records of methane gas produced. This can be accomplished by placing an orifice plate in the gas pipe flow stream and measuring a differential pressure across the orifice plate. The measured differential pressure together with other known or measured items such as temperature and pipe size can be used to determine the methane gas flow rate.
It is known that orifice plates in many or all of the landfill well gas lines in landfill methane recovery wells are retained to control overall pressure and flow of the methane gas. If the measured differential pressure across the orifice plate exceeds a predetermined value, action may be required to 1) lower the differential pressure so that size and operation of the site vacuum pumps is not impacted, and/or 2) increase the overall flow rate to maximize the recovered volume of methane gas. Well gas flow status should be measurable without impacting the well environment. Known orifice designs provide for one or more orifice sizes in orifice plates that require a coupling to be disassembled to add or change the orifice plate. Well environments may be hazardous because of flammable gasses such as methane, or chemicals in the leachate that corrode or damage test equipment. Measurement systems that require the well to be opened to atmosphere for differential pressure measurement are therefore undesirable, particularly in wells operating under a vacuum, to prevent outside air entering the well and/or methane gas release. In addition, opening the well or disassembling components that open the well for methane gas flow measurement can by itself affect the well level, and thereby adversely impact methane recovery in methane recovery wells.